paper 2 Flashcards
what does the nitrogen cycle show
how nitrogen is recycled into ecosystems
why do plants and animals require nitrogen
in order to produce proteins and nucleic acids
what percentage of the earths atmosphere is nitrogen gas
78%
what are the 4 key processes of the nitrogen cycle
- nitrogen fixation
- ammonification
- nitrification
- denitrification
explain the 4 points of nitrogen fixation
- atmospheric nitrogen gas is converted into nitrogen containing compounds
carried out by nitrogen fixing bacteria - the bacteria converts nitrogen into ammonia which forms ammonium ions that can then be used by plants
- these nitrogen fixing bacterias are found inside the root nodules of leguminous plants (peas,beans,clovers)
- the bacteria have a symbiotic relationship with the plants
bacteria provide nitrogen containing compounds
plants provide organic compounds such as carbohydrates
explain ammonification
- nitrogen compounds in waste products and dead organisms are converted into ammonia by saprobrionts
- the ammonia forms ammonium ions in the soil
explain nitrification
- ammonium ions in the soil are converted by nitrifying bacteria into nitrates
- initially nitrifying bacteria convert ammonium ions into nitrites
- different nitrifying bacteria then convert these nitrites into nitrates
explain denitrification
- denitrifying bacteria use nitrates in the soil during respiration
- this process produces nitrogen gas, which returns to the atmosphere
- process occurs in anaerobic conditions
Describe the role of receptors and the nervous system in increasing heart rate during exercise.
• Chemoreceptors detect a rise in acidity/fall in pH
• Baroreceptors detect a rise in blood pressure
• Send impulses to medulla;
More impulses to SAN
• Chemoreceptors -
Via the sympathetic NS;
• Baroreceptors -
Via the parasympathetic
NS.
Describe how the mark, release, recapture method could be used to determine the size of a population.
Collect a sample, mark and release;
Leave time for sample to disperse before a second collection;
Population = (number in
first sample x number in second sample) / number of marked in second sample.
What is a gene pool?
All the alleles in a population
Describe sympatric speciation.
Species are not
geographically isolated;
Mutations cause differences;
Reproductive separation/ no gene flow/ gene pools remain separated;
Different alleles are passed on and the frequency of alleles changes;
Disruptive selection;
Eventually, different species can’t interbreed to produce fertile offspring.
What is the difference between interspecific and intraspecific competition?
Intraspecific competition:
Occurs between individuals of the same species. E.g. two oak trees competing for sunlight or two male deers competing for a mate.
Interspecific competition:
Occurs between individuals of different species. E.g. a leopard and a lion competing for a common prey.
What is the function of acetylcholinesterase?
Acetylcholinesterase catalysed the hydrolysis of ACh into acetate and choline;
Choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh;
ACh is then packaged into presynaptic vesicles ready to be used when a new action potential arrives.
Describe what happens if acetylcholinesterase is inhibited.
Less acetylcholine broken down;
Acetylcholine attaches to receptors;
More sodium ions enter to reach the threshold for depolarisation/ to trigger an action potential.
Describe the role of calcium ions and ATP in the contraction of a myofibril.
Calcium ions diffuse into myofibrils from sarcoplasmic reticulum;
Causing movement of tropomyosin on actin;
This causes exposure of binding sites on actin;
Myosin heads attach to these binding sites;
Hydrolysis of ATP causes myosin heads to bend;
Bending pulls actin molecules and attachment of a new ATP molecule to each myosin head causes them to detach from actin binding sites.
Give two ways in which ATP is a good energy source for cells to use.
ANY 2 FROM
Releases small amounts of energy;
Releases energy instantaneously;
Phosphorylates other compounds to make them more reactive;
Can be rapidly resynthesised;
Doesn’t leave cells;
Little energy is lost as heat.
Osmoreceptors are specialised cells that respond to changes in the water potential of the blood.
Where would you find osmoreceptors in the human body?
Hypothalamus
Describe what happens during photoionisation in the light-
dependent reaction.
Chlorophyll absorbs light/ Light excites electrons in chlorophyll;
Electrons are lost/ Chlorophyll becomes positively charged/
Electrons go to the electron transport chain.
Explain the advantage of having different coloured pigments in leaves.
Absorb different/more wavelengths of light for photosynthesis.
Heat stress decreases the
LDR of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.
Less/no ATP;
Less/no reduced NADP.
Where is rubisco found in the cell?
Stroma
Name the features of a calorimeter that enables a valid measurement of the total heat energy released.
Thermometer;
Stirrer distributes heat energy;
Insulation reduces loss or gain of heat/reduces conduction;
Water has high specific heat capacity.
Name the two products of the LDR that are required for the calvin cycle.
ATP;
Reduced NADP.
